Process for the preparation of alumina



' Patented Oct. 13, 1931 STATES.

r ii'itoonss ron THElPREPAlRATiOfi ori inuiur vni" l v No Drawing. Application filed October 4, 192 9, Serial'iibl 1%???)1191 2, and in Austriafseptemb erl i, fig

' T his invention relates to the preparationof alumina from bauxite, and has for its ob ject to provide an improved process for this purpose.

For preparing alumina from bauxite it is known. to treat the bauxite with a liquid calied aluminate lye which is obtained in the following manner When starting the process, bauxiteis decomposed by the. action of a caustic soda solution; the solution, after having been used for this purpose, contains sodium hydroxite, varying quantities of sodium aluminateand-a small amount of sodium carbonate; this liquid isvery suitable N for decomposing further quantities of bauxite provided the ratio of A1 0 Na Obe 1: 4;, 5 up to 6; A liquid being thus composed will be hereinafter referred to as aluminate' According to the known process of K. J Bayer bauxite is treated attemperatures' of loll-172 and-at a pressure of 6 to 7 atmlwith alinninate lye of -44 Bnin an autoclave for from one and a half up to two hours.

25 The liquid is then diluted to about 20-24; Be,

filtered off from the substances (red slime) notdissolved, then inoculated with alumina hydrate and stirred thus causing the alumina hydrate to'separate from the solution. v

T he liquid. after being filtered from the solid precipitate is concentrated to 44 B.

by evaporation and is then ready to be used aga The continuous dilution and repeated evaporation of the liquid is, however, a'techmeal and economical disadvantage of the process, which means much work, a great expenditure of heat, and, in addition to a considerable requirement of space,'also involves the high costs of manufacture; 7

use no liquid of higher cOncentrationthan 38 Be; at the utmost,rthat is .of'the specific gravity of 1, 36;thus', however, the dilution men s have also been described for carrying out the decomposition at about 170 with the aluminate lye of 22,B. ,VVe have, however, ascertained that this lye at 170does an composition.

WOLF JoHANNEs i'ILLEn Am) HEINRidH, IiiLLER, or views, iA- USTBIAQ.

'drate the yield of soluble alumina can be li 'ar xempl s is ampedbytametenements lye of -22--B. at 200 (lg-the pressure at th s bauxite, the d composition ,beingmracti Hy The proposition has already been made to and evaporation is not avoided Experi-V not permit of any technically sufiicient'de I v jTioknflflngflg 3,5

ll/ e have now discovered, that decoinposition of thebauxite can be efie'c'tedeven with. an alunii'n'at'e lye of abOutQO-QEZ BZ, if the decomposition is carried out above about 190 *'C.,; the pressure". being' at this temperatureautomatically increased to about; v

'l0-15 "atni; or""higheri f-Th'e corresponding pressure thus obtained isjustsuflicient'to per mu; ebullient boiling of the solution at' the choseiifteniperature':

brought to'about 1 :11, f8 asusuall. e

lt'isgknown thattthecompositio ofthe alumina hydrate present ini thefbauxiteis different according to the origin of the tum; l In consequence ofthis diiferen' c'e ofthe' mblecular construction of the i alumina hy brought to the same amount by ,using diife'r 'ent temperatures-of the decofr'l posiirg liquid.w I

temperature amounts tol8 atmm The yield is 96 'per cent. of thealumina contained inthe,

complete.

' The improvement may b's'eenjrrom a com- -'parison with the old process, by which only.

per cent. of the-alumina present in'the bauxite are obtained. 7

Example 2.A bauxite from Hungary of the following composition: 7

is Percent ido is decomposed with an aluminate lye of 22 B. at 230 C. and a pressure of 25 atm. The output of alumina is 62 per cent. when the temperature is raised to 280-290 C. and the '5 pressure to 100 atm. 93 per cent. of the alumina contained in the bauxite are obtained. The known process of Bayer only yields per cent. alumina. The process may be carried out in practice by working in an autoclave either discon tinuously as usual in the known processes or, in a more advantageous modification, by working continuously. The autoclave may II for instance be shaped in the form of a heatingcoil withinwhich the mixture of bauxite V and aluminate lye is kept. in continuously p ss e' viemen y m o h pressure pump'and leaves the reaction chamher through a weighted valve or counter pressure pump. In thisarrangement the heat cont ained in the mass may be used for preheating thestarting mixture. The red slime is separated i from the solution in the usual manner, for instance by a continuously working filter and the alumina vhydrate caused to separate [from the solution,v from. which removed a manner known per se. I The-residual aluniinatelye obtained after a. 8!) separation of the precipitated hydrate is led back into circulation without concentration, the washing liquid either serving for the preparation'of fresh caustic soda solution, whichcan hearsed for providing the necessary causticsoda aniount, or being concentrated by evaporation .to the concentration of 20-22" B': a

What we c l a r is:v

1. A process for preparing alumina from m bauxite, "which. comprises heating bauxite with'aluminate lye of approximately 20 to 22 B. at temperatures above 190C. and corresponding pressures until the dBCOIll-z position of the bauxite is substantially completef a 2. A process for preparing alumina from bauxite, which comprises heating bauxite with aluminate lye of approximately 22 at temperaturesabove 190 C. and corre- 5p spending/pressures. until the decomposition of the bauxite is substantially complete; a In testimony. whereof wealfix, our signatures.

WOLF JOHANNES MT ILLER. HEINRICH HILLER. 

